Concentration-dependent characteristics of a complex coacervate

In this work, we have comprehensively and systematically investigated the influence of the initial concentration of oppositely charged polyelectrolyte solutions on the interaction strength, interfacial tension and local structure of the coacervate phase generated at charge stoichiometry in a PDADMAC/PANa model system. We have shown for the first time that the concentration has a direct and significant impact on the complexation strength between the two polyelectrolytes, leading to lighter coacervates with constant mass yield and increasing network mesh and decreasing liquid-liquid interfacial tensions until a critical concentration where oppositely charged chains no longer interact, generating the so-called self-supressed coacervate single phase (SSCV). An effect that is due the free counterions present in the solution, whose concentration increases with that of the PE polyelectrolytes and gradually screens the electrostatic complexation. These characteristics will certainly have an impact on the capacity of these coacervates, objects of great scientific and technical interest today, to be efficiently stabilized, to encapsulate active principles and to serve as bioreactors.